I'd argue that it would be best to lock the whole DF section, but keeping it up as a reference, if possible. And putting a big fat notice for any recent newcomers to direct them to the official forums.

The reason is that DF is after all Toady's livelyhood, and if I were him I would prefer if there wasn't two almost identical forums devoted to my game, only one of which I had any kind of control over. Bug reports, suggestions etc would be much more useful in the official forums.

Regardless, it would probably be a good idea to make it abundantly clear to any recent newcomers that these aren't the official forums. The identical layout and use of the bay12games DF logo might otherwise give that impression. Which wasn't a huge deal while the official forums were down, but if they're going up again I think it might be.